LS3 Heads and Cam Test - Heads Up!

Are Ported Heads Worth More Power Than A Cam Swap On The LS3?

Even the competition has to agree, Chevy's LS-engine family is more than just a worthy successor to the original small-block; it's one hell of a motor. The Blue Oval boys are jumping up and down about their new 5.0L, but (as usual) they are still behind the eight ball in terms of displacement and power output. While the new four-valve 5.0L mod motor offers reasonable high-rpm power, it is decidedly lacking in low-speed power compared to the LS3. Credit the 6.2 liters of displacement for all that wonderful torque. High rpm power is all well and good, but the vast majority of spirited (street) driving comes lower in the rev range. Besides, in the LS3 there is no choice between low-speed and high-rpm power, as the GM motor offers both. Toss in the fact that the LS3 features lightweight, all-aluminum construction, a composite intake, and even variable cam timing (in the automatic/L99 version) and you have a small-block with all the technology of a DOHC motor, without the penalties in size, weight, and complexity. Back in the original muscle car era, it took a big-block to muster power ratings that exceeded 400 hp and a like amount of torque-using those old (gross) power ratings and not net! The modern LS motor makes this a good time to be a Chevy owner.

2/25

The LS engine family has evolved constantly to keep GM ahead of the competition. The original LS1 was a solid step above the LT1, just as the LT1 easily eclipsed the performance of the previous L98 TPI motor. In its latest form, the LS3 has followed the 5.7L LS1/LS6 and 6.0L LS2 engine configurations by starting with an increase in displacement, checking in at 6.2 liters. This came courtesy of an increase in bore from 4.00 inches (in the LS2) to 4.065 inches, though the two shared the same stroke of 3.622 inches. The increase in bore size not only upped the displacement, but also airflow, as head flow increases with bore size. Combine this with a revised cylinder head that replaced the cathedral-port design with a more conventional rectangular port, and you have the makings of one serious small-block. Tested on the flow bench, production LS3 heads flow as much as 315 cfm right out of the box. Not long ago it took a pretty serious 23-degree small-block head to achieve these same flow numbers, offered by the stock LS3. Despite flow figures that suggest supporting over 600 hp (we recently made 690 hp with a set of stock LS3 heads on a 468 stroker for our sister book Hot Rod), additional flow is available with proper porting. What we wanted to find out was just how much power was available with a set of ported LS3 heads.

3/25

The massive head flow offered by the stock rectangular-port heads means the LS3 responds favorably to cam swaps (Ed note: "favorably" is an understatement!). The flow potential of the stock heads allowed GM to reach its power goals for the production LS3 using relatively mild cam timing, akin to the early LS6 (and LS2) grind. Using the same 204/211 duration split (measured at .050), the stock LS3 cam offers .551/.522-inch lift with a wide lobe separation angle of 117 degrees. This combination of mild cam timing and sizable head flow means the LS3 motor is just begging for wilder cam timing. Think of the LS3 as an all-aluminum race motor without the race cam. Swapping in the right cam will literally transform your mild-mannered stock motor into a street screamer, but where does that leave ported heads? Will even more head flow improve the power output with the stock cam? Are the gains offered by ported heads greater after you've performed a cam swap? Is porting worth the extra expense? That's what we came to find out.

4/25

To illustrate the potential lurking in the LS3, and to answer the cam versus cylinder head question, we embarked on a series of tests using a GMPP LS3 crate motor. Performing the multi-head and cam swap on the engine dyno was much easier than had the LS3 been installed in a '10-or-newer Camaro. To illustrate the gains offered by both head and cam swaps, we ran the GMPP LS3 crate motor on the engine dyno in stock trim, then after the installation of a set of GMPP CNC LS3/L92 heads followed by a Comp LSr hydraulic roller cam. To finish things off, we installed one final set of dedicated LS3 castings from ProComp Motorsports. This way, we compared ported stock castings to a set of (affordably priced) aftermarket LS3 heads. Before we could run the GMPP LS3 on the engine dyno, a few changes were necessary. Off came the factory drive-by-wire throttle body and on went a more dyno-friendly manual throttle body from FAST. The stock exhaust manifolds were also replaced by a set of 1 3/4-inch, long-tube headers. The production water pump was likewise ditched in favor of a Meziere electric unit (the LS3 ran sans accessories).

MORE PHOTOS

VIEW FULL GALLERY

xclose

LS3 Heads and Cam Test - Heads Up!

The head and cam tests were run on a GMPP LS3 crate motor. Pulled right from the assembly line, the LS3 offered a combination of quality, performance, and reliability that can only come at the OEM level.

Prior to running the LS3 on the engine dyno, it was necessary to replace the factory drive-by-wire throttle body with a manual 102mm version from FAST.

Though the crate motor included factory exhaust manifolds, all testing was performed with a set of 1 3/4-inch long-tube headers feeding 18-inch collector extensions. The headers were drilled for individual oxygen and temperature sensors, though we did not utilize them on our test motor.

Making our life easy was a complete Holley Dominator EFI engine management system that plugged right into the factory injectors, sensors, and coil packs. Westech's Ernie Mena was responsible for optimizing the tune on each combination.

After a break-in cycle, we ran the motor in crate-motor form to establish a baseline. Run with no accessories, long-tube headers and an optimized tune, the LS3 produced 493 hp and 485 lb-ft of torque.

First up was a set of CNC-ported heads from GMPP. The GMPP heads featured extensive porting on the intake side that improved the flow rate by 30-40 cfm per runner. The question now was would the stock motor be able to take full advantage of all that extra airflow?

The exhaust port received equal attention, though the intake-to-exhaust flow relationship was still skewed in favor of the intake. This is why motors equipped with LS3 heads respond well to dual-pattern cam profiles with plenty of exhaust duration.

All of the combinations were run with the factory 1.7:1 ratio rockers. Additional power is available with a swap to true roller rockers (especially with additional ratio), but make sure you have sufficient valve spring pressure as the aftermarket rockers are generally heavier than their factory counterparts.

The CNC-ported heads from GMPP came equipped with stock LS3 springs. These were woefully inadequate for the cam swap we had planned, so they were upgraded to a stronger set. When purchasing the GMPP CNC heads, better figure on a spring upgrade if you plan on running them with anything other than the stock cam.

For our future cam upgrade, we replaced the stock springs with a set of 918 springs from Comp Cams.

Run with the GMPP CNC heads, the power jumped only slightly from 493 hp (and 485 lb-ft) to 505 hp (and 498 lb-ft). What the heads really needed was more motor to take advantage of the extra airflow.

Next on the list for our GMPP crate motor was a cam swap. Out came the factory cam to make room for the Comp LSr grind. Cam swaps on the LS motors are a joy compared to a conventional small-block Chevy.

The LS3 featured a single-bolt cam, while our Comp 281LRHR13 featured the earlier 3-bolt flange. The key was to replace the single-bolt LS3 cam sprocket with a 3-bolt LS2 (which featured the required cam sensor provisions).

The new Comp cam was bolted in place on the dyno. A big step up from the stock LS3 grind, the 281LRHR13 cam offered a .617/.624-inch lift and 231/239 duration split with a 113-degree lobe separation angle.

Care must be taken when choosing a cam for the LS3, as the factory flat-top pistons did not feature valve notches. The 281LRHR13 cam was about as wild as we dared go and still retain sufficient piston-to-valve clearance.

Equipped with the new Comp hydraulic roller cam, the GMPP-headed LS3 pumped out impressive power numbers, jumping from 505 hp and 498 lb-ft to 567 hp and 519 lb-ft. Further indicating the cam was an excellent choice, there was no trade off in low speed power with the Comp cam-it equaled or exceeded the power offered by the stock cam from 3,000 rpm past 6,500 rpm.

The final test was to compare a set of dedicated LS3 castings from ProComp Motorsports to the ported stock castings from GMPP. In reality, the test motor was a tad on the tame side for this test, as either head offered enough flow to support 650 hp. The CNC intake port of the ProComp head flowed 360 cfm.

Knowing most LS3 enthusiasts would be teaming their ported heads with a healthy cam, the CNC heads from ProComp Motorsports featured a spring package that offered 140 pounds of seat pressure and 360 pounds of open pressure. Further improving the rpm capability was a set of lightweight titanium retainers.

The new LS3 heads from ProComp Motorsports offered some gain over the GMPP heads, though a jump from 567 hp to 573 hp is not terribly significant. Just as our first test showed when we installed the GMPP heads on the stock motor, the crate motor (even with the cam) was simply not stout (or large) enough to take full advantage of the tremendous head flow. We have exceeded 720 hp with these heads from ProComp Motorsports on a wilder 468 stroker, but much of their airflow went unused on this LS3.

Stock LS3 Heads vs GMPP CNC LS3 Heads
Given the already adequate flow rate of the stock LS3 heads, it was not surprising that replacing them with CNC-ported versions from GMPP was worth only minor power gains. Run with the stock cam, the head swap improved the peak power output from 493 hp and 485 lb-ft of torque to 505 hp and 498 lb-ft of torque. Something we did not expect was an increase in power throughout the rev range. The largest torque gains came from 4,000 rpm to 4,500 rpm, but the gains were pretty consistent elsewhere. The reason for the limited power gains had nothing to do with the airflow potential of the GMPP heads, but the fact that the stock LS3 heads flowed so well already. Combine the impressive flow with a (low-lift) stock cam and you severely limit the power gains offered by the GMPP CNC-ported heads. Even more than the stock LS3 heads, the GMPP CNC heads need a healthy cam profile to strut their stuff.

Stock LS3 Cam vs Comp Xtreme Energy Cam
Cam swaps should be considered mandatory for any LS3 owner. The hydraulic roller Comp LSr profile featured a .617/.624 lift split, a 231/239 duration split (at .050) and a 113-degree lobe separation angle. Naturally the ported heads responded very well to the high lift supplied by the new cam profile. The cam swap improved the power output of the LS3 from 505 hp and 498 lb-ft to 567 hp and 519 lb-ft. Another sign that LS3 motors need wilder cam timing is the fact that (despite the healthy cam specs) the hydraulic roller cam never lost out to the factory cam, even down at 3,000 rpm.

GMPP CNC Heads vs ProComp Motorsports Heads
The final test run was to evaluate a set of dedicated aftermarket head castings for the LS3. Available from ProComp Motorsports, the LS3 heads offered impressive flow numbers (360 cfm at .700). The flow numbers suggest these heads will support over 700 hp on the right combination, and our milder combination could not take full advantage of the extra airflow. The peak numbers jumped from 567 hp and 519 lb-ft to 573 hp and 520 lb-ft, with gains available only at the top of the rev range. What this does suggest is that the ProComp heads are at least the equal of ported stock heads and that the combination of ported heads and a cam will really wake up an otherwise stock LS3.